Impact Of Different Positive End-Expiratory Pressures On Lung Mechanics In The Setting Of Moderately Elevated Intra-Abdominal Pressure And Acute Lung Injury In A Porcine Model

The effects of a moderately elevated intra-abdominal pressure (IAP) on lung mechanics in acute respiratory distress syndrome (ARDS) have still not been fully analyzed. Moreover, the optimal positive end-expiratory pressure (PEEP) in elevated IAP and ARDS is unclear. In this paper, 18 pigs under general anesthesia received a double hit lung injury. After saline lung lavage and 2 h of injurious mechanical ventilation to induce an acute lung injury (ALI), an intra-abdominal balloon was filled until an IAP of 10 mmHg was generated. Animals were randomly assigned to one of three groups (group A = PEEP 5, B = PEEP 10 and C = PEEP 15 cmH(2)O) and ventilated for 6 h. We measured end-expiratory lung volume (EELV) per kg bodyweight, driving pressure (Delta P), transpulmonary pressure (Delta P-L), static lung compliance (C-stat), oxygenation (P/F ratio) and cardiac index (CI). In group A, we found increases in Delta P (22 +/- 1 vs. 28 +/- 2 cmH(2)O; p = 0.006) and Delta P-L (16 +/- 1 vs. 22 +/- 2 cmH(2)O; p = 0.007), with no change in EELV/kg (15 +/- 1 vs. 14 +/- 1 mL/kg) when comparing hours 0 and 6. In group B, there was no change in Delta P (26 +/- 2 vs. 25 +/- 2 cmH(2)O), Delta P-L (19 +/- 2 vs. 18 +/- 2 cmH(2)O), C-stat (21 +/- 3 vs. 21 +/- 2 cmH(2)O/mL) or EELV/kg (12 +/- 2 vs. 13 +/- 3 mL/kg). Delta P and Delta P-L were significantly lower after 6 h when comparing between group C and A (21 +/- 1 vs. 28 +/- 2 cmH(2)O; p = 0.020) and (14 +/- 1 vs. 22 +/- 2 cmH(2)O; p = 0.013)). The EELV/kg increased over time in group C (13 +/- 1 vs. 19 +/- 2 mL/kg; p = 0.034). The P/F ratio increased in all groups over time. CI decreased in groups B and C. The global lung injury score did not significantly differ between groups (A: 0.25 +/- 0.05, B: 0.21 +/- 0.02, C: 0.22 +/- 0.03). In this model of ALI, elevated IAP, Delta P and Delta P-L increased further over time in the group with a PEEP of 5 cmH(2)O applied over 6 h. This was not the case in the groups with a PEEP of 10 and 15 cmH(2)O. Although Delta P and Delta P-L were significantly lower after 6 hours in group C compared to group A, we could not show significant differences in histological lung injury score.